# Blown resistor identification

#### stvmcmlln

Joined Jan 28, 2023
5
Hi Folks!
I have found a blown resistor in a battery charger. Is anyone able to help identify what value is should be replaced with?
Pictures of the circuit board back and front attached.
Many thanks in advance!

stv

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#### ericgibbs

Joined Jan 29, 2010
17,136
hi stv,
Welcome to AAC.
What is the AC input voltage on that charger PCB.?
E

#### Dodgydave

Joined Jun 22, 2012
10,681
Can you take it out and see if the other side is ok so we can read it, at a guess it could be 47ohms?

#### stvmcmlln

Joined Jan 28, 2023
5
hi stv,
Welcome to AAC.
What is the AC input voltage on that charger PCB.?
E
Hi Eric, the PCB is connected to a 240v wall plug. I’ve added a picture of the writing on the plug.
Thanks so much!
stv

#### stvmcmlln

Joined Jan 28, 2023
5
Can you take it out and see if the other side is ok so we can read it, at a guess it could be 47ohms?
Hi Dave,
The resistor is scorched all the way around so none of the bands are readable unfortunately.
Thanks for your help.
Perhaps I should just try a 47ohm resistor?
stv

#### BobTPH

Joined Jun 5, 2013
6,291
Don’t do that! We now know the voltage and current output if the power supply. If yoy can tell us the battery voltage, we can compute the resistor.

#### Dodgydave

Joined Jun 22, 2012
10,681
Hi Dave,
The resistor is scorched all the way around so none of the bands are readable unfortunately.
Thanks for your help.
Perhaps I should just try a 47ohm resistor?
stv
We need to know what voltage the battery is, the charger says 14V battery and outputs 17.4V, so it's possibly dropping 3V ...so 47 ohms will give you a current of 63mA.
You need to check the diodes to see if they are not blown too

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#### BobTPH

Joined Jun 5, 2013
6,291
I am going to guess the battery is NiCad given the simplistic charger. And it is a 0.1C trickle charger, i.e. it takes about 12H for a full charge.

#### dl324

Joined Mar 30, 2015
15,510
Perhaps I should just try a 47ohm resistor?
It's a 5% tolerance resistor, so the significant digits can only be 43 or 47. If you could make out the 3rd band, that would tell you if it's 4x, 4.x, 0.04x.

What is the capacity of the battery being charged? It must be a NiCd, probably being charged at 0.1C because there's no charged detection.

#### stvmcmlln

Joined Jan 28, 2023
5
Thanks for the responses! Here’s a pic of the battery. It’s an aftermarket battery.

#### dl324

Joined Mar 30, 2015
15,510
Thanks for the responses! Here’s a pic of the battery. It’s an aftermarket battery.
That's not a very good charger for a 14.4V NiCd battery. Fully charged, it would be 16.8V and the adapter is only outputting 17.4V. You'll lose 1.4V in the bridge rectifier, so there's not much voltage left to charge the battery.

Did the charger burn up because you tried to charge a bad battery, or one with a low voltage?

I'd try a 47 ohm 3W resistor. Charging a dead battery would make it dissipate 6W. It would be okay down to around 5V.

#### stvmcmlln

Joined Jan 28, 2023
5
That's not a very good charger for a 14.4V NiCd battery. Fully charged, it would be 16.8V and the adapter is only outputting 17.4V. You'll lose 1.4V in the bridge rectifier, so there's not much voltage left to charge the battery.

Did the charger burn up because you tried to charge a bad battery, or one with a low voltage?

I'd try a 47 ohm 3W resistor. Charging a dead battery would make it dissipate 6W. It would be okay down to around 5V.
Thank you! I’ll try that.